The look is created in the second step. That is the “base transform look”, and yes it does not need any tweaks to viewing conditions or anything else like that. Very much subjective step.
The first step is the scaling step which also creates the appearance match. That is what Nick and I were talking about. The first step is the technical step, or one could call it even a normalization step, and that then allows the second step to not need any tweaks, even though the output is for different displays.
I could not figure out how to do both in one step (at least not in invertible way, the very first version did that, but was very naive and not invertible)).
What do you mean by sensitive? Do you mean it compresses them clearly different amount or that it has to, or something else?
I believe the previous chroma compression version was actually doing something like that. It wasn’t the linear ratios of the tonescale itself, but another similar curve. It’s the one I linked in the first post. That thing is too complicated but I could probably come up something much simpler now, but still more complicated than the current approach. Simplicity was the reason why I switched…